New lad is keeping nothing in except something for the windsurfer (9)
I believe the answer is:
sailboard
'something for the windsurfer' is the definition.
(board used by a windsurfer)
'new lad is keeping nothing in except' is the wordplay.
'new' is an anagram indicator.
'keeping' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
'in' means one lot of letters goes inside another.
'except' becomes 'bar' ('bar' can mean 'except' or 'not including').
'lad'+'is'='ladis'
'ladis' anagrammed gives 'saild'.
'o' inserted within 'bar' is 'boar'.
'saild' enclosing 'boar' is 'SAILBOARD'.
(Other definitions for sailboard that I've seen before include "Plank for windsurfing" , "Windsurf" .)